1. Field of the Invention
The present invention relates generally to prosthetic joints and, more particularly, to a modular prosthetic knee joint construction which provides tibial wedges to compensate for a broad range of types and sizes of medial/lateral and anterior/posterior bone deficiencies.
2. Description of the Prior Art
The knee joint basically consists of the bone interface of the distal end of the femur and the proximal end of the tibia. Appearing to cover or at least partially protect this interface is the patella which is a sesamoid bone within the tendon of the long muscle (quadriceps) on the front of the thigh. This tendon inserts into the tibial tuberosity and the posterior surface of the patella is smooth and glides over the femur.
The femur is configured with two knob like processes (the medial condyle and the lateral condyle) which are substantially smooth and articulate with the medial plateau and the lateral plateau of the tibia, respectively. The plateaus of the tibia are substantially smooth and slightly cupped thereby providing a slight receptacle for receipt of the femoral condyles.
When the knee joint is injured whether as a result of an accident or illness, cartilage covering the natural bones may become damaged to the extent that they are unable to function (articulate) properly. If the bones are affected beyond the level or degree where natural healing and new growth will remedy the damage, then a prosthetic replacement of the damaged portion is called for in order to relieve pain and to restore normal use to the joint. Typically the entire joint is replaced by means of a surgical procedure which involves removal of the ends of the corresponding damaged bones and replacement of these ends with prosthetic implants. A typical such implant would be for the hip joint wherein a metal implant could be anchored in the intramedullary canal of the femur and would provide a generally spherical protuberance extending outwardly therefrom. The mating prosthetic portion would be a polyethylene socket member suitably anchored into the acetabulum. While prosthetic devices of this type, normally including a physiologically inert metal member and an engaging high density polyethylene member, are well known in the art, these types of devices are of a fixed and unchanging nature once they are inserted (implanted) into the patient and anchored there, whether by pinning or by acrylic bone cement or both.
Due in part to the fact that the size, shape and anatomy of virtually every patient is different, great care must be taken by the orthopedic surgeon in order to select properly sized and shaped prosthetic members for implanting. In order to achieve a suitable fit and size compatibility, an extensive number of a variety of each type of prosthetic implant must be available to the orthopedic surgeon from which he may choose. As a result, the cost of inventory as well as the logistics of ordering and storing a wide variety of prosthetic implants is cumbersome. Therefore, it would be an improvement to this present situation if prosthetic devices could be structured with removable portions such that there would be a reduction in inventory without a corresponding compromise as to the number and variety of different prosthetic combinations which can be created. In order to provide such an improvement, it is necessary that the prosthetic portions which are to be mixed and matched into a variety of combinations be suitably secured together so that the prosthetic member, which they in combination create, is not weaker nor more likely to fail than would be a similar prosthetic member constructed as a single integral piece.
A further concern involves the procedure when a prosthetic device becomes worn or damaged and a replacement must be made. While this is possible, it oftentimes involves elaborate surgery depending upon the particular portion of anatomy involved and the extent or nature of the damage to the prosthetic device. Furthermore, certain portions of the anatomy such as knee joints may be more susceptible to wear due to the surface area of articulation, the nature of the anatomy and the typical loads and forces which are encountered by this particular joint. Repair and/or replacement may also be desired when interfacing portions of the anatomy change and the contacting portion of the prosthesis needs to be revised as to its shape or size.
By structuring a prosthetic implant such that the portion most likely to wear or desired to be changed is quickly and easily replaceable from the remaining portion of the prosthetic implant, significant amounts of surgical time can be saved and the prosthesis can be more closely tailored to the patient's needs. Equally important is the fact that the portion of the prosthesis which is anchored into the patient, such as a tapered shaft inserted into the intramedullary canal of the tibia or of the femur, does not have to be surgically removed in order to make a replacement of a worn or damaged tibia articulation portion. Such a replaceable concept, in order to be effective, must securely hold the anchored portion and the replaceable portion together so as to act as an integral member regardless of the nature or complexity of the forces and loads acting thereon. With a design which achieves the requisite strength and durability, it is then possible to mix and match the replaceable portion with various anchored portions and vice versa such that, for example, an inventory of five relatively large and expensive replaceable portions and five relatively small and inexpensive anchoring portions for a tibial or femoral implant would be able to provide 25 different combinations of each to the orthopedic surgeon rather than having to inventory and stock 25 separate complete relatively large and expensive portions.
Often included among the components used in a prosthetic knee joint system is a wedge employed to correct for naturally occurring or disease-caused or injury-caused unevenness of the tibial bone. In one instance, there may be an anterior/posterior deficiency on the tibia; in another instance there may be a varus/valgus deficiency; or there may be one or the other but present only in one compartment of the knee joint, that is, in the lateral compartment or in the medial compartment. The wedge compensates for the deficiencies and assures that, following implantation, the patient will eventually be able to stand and walk erect.
Tibial and femoral primary or revision knee prostheses that are presently being marketed often times have a fixed central stem, located on the distal plane of the tibial tray, or component, and on the proximal portion of the femoral component's anterior/ posterior box. This stem is used primarily for purposes of stabilization and strength, both during installation and after the joint has been rebuilt. It may be difficult to determine prior to surgery, even radiographically, the size of the stem to be used. As a result, it is often necessary to wait until the bone structure is personally viewed by the surgeon during the implant operation before selecting the proper size of the implant, including a wedge, if required.
While wedges are known and commonly used, their use in a modular system offering the surgeon a variety of other options is not generally known. One important feature sought by the surgeon is a choice of the mode of fixation. While some surgeons prefer to use cement exclusively, others use bone screws, and still others prefer a combination of the two.
Although numerous devices and systems are presently known which generally satisfy the goals for which they were intended, none offer the simplicity, economy, accuracy, and options to the surgeon which are achieved by the present invention.